I work at a library, so I got piles when they weeded 'em. And then a former coworker had her husband, who still works with us, pass on to me the Animorph weeds from where she now works.
The other huge find I made was at a local used book shop that I wish still existed but it doesn't. Someone had donated an entire box of Animorphs. But what I don't get was why they had two or so of most of the books in the box.